(1) Field of the Invention
This invention relates generally to braking devices and, more particularly to a disk brake mounting apparatus and method.
(2) Prior Art
The prior art teaches a "floating head" disk brake wherein there is a single piston supporting one friction element, a housing supporting the other friction element and the housing is mounted for sliding action on a fixed support member transversely to a rotor disk for braking engagement therewith. There are various known means for achieving the slidable movement between the disk brake housing and the support structure. For example, yieldable means in the form of flexible straps can couple the support structure with the slidable housing so that the slidable housing is supported on the support structure for slidable movement relative thereto by the flexible straps. In order to actuate the brakes and bring each of the brake shoes into engagement with opposite sides of the rotor, the flexible straps must flex in a direction generally perpendicular to the plane of rotation of the rotor to be braked. In these prior art devices, there is resistance to the movement of the housing due to the physical characteristic of the flexible straps due to the necessity for bending the straps with a certain amount of force. Also, due to the characteristics of the flexible straps there is a certain amount of hysterisis involved so that the housing may not return to its original position when a braking system is relaxed.
Attempts have been made to improve the performance of these flexible straps by having loops positioned therein which permit the ends of the springs, which support the housing on the support structure, to move relative to each other by a rolling movement of the loop formed in the spring. This rolling action reduces the resistance to movement and hysterisis effect. Nevertheless, any such improvement is achieved with additional complexity and cost, and does not provide a desirable solution to the problem.
Another prior art disk brake design includes a sliding action wherein pins are rigidly mounted to a floating brake shoe housing and semicircular receiving grooves, for the pins, are located in the stationary support member with sufficient tolerances between the pin and the grooves to allow reasonably free sliding action therebetween. This type of design has been known to produce excessive brake rattle during normal driving. To solve the rattle problem, members have been added to exert forces against the pin elements to pre-clude rattle between the pin elements and the slots located in the arms or support members. Although this technique reduces the rattle problem, the force against the pin elements by the pressure members introduces an undesirable resistance to lateral sliding of the pin elements, and thus, also, of the caliper housing.
This resistance to lateral sliding cause a condition frequently referred to in the disk brake industry as "drag", "knock-back" or "shake-back". Drag results from the brake lining being held against the disk due to the resistance to lateral sliding. Drag is objectionable because it increases wear and fuel consumption. Knock-back results from a deflection or wandering of the brake disk or rotor which engages a brake lining and friction member and thus the piston, forcing the piston back into its associated cylinder. Knockback is objectionable and requires upon the next brake application, that the brake pedal travel an unnecessary distance for the brake piston friction member to again grip the rotating disk.
The prior art also teaches a coupling between the disk brake housing and the support structure wherein the housing has rigidly secured thereto a pin element which is slidingly retained by a sleeve element. The pin element and sleeve element in combination provide a bearing member for the support structure which floatingly and slidingly carries the housing for movement in a direction transverse to the plane of the rotor. Springs secure the sleeve to the support structure. When the sleeve and spring combination is used, the sleeve must be sufficiently strong to support the pin and the springs must be sufficiently strong to retain the sleeve so that the sleeve does not come free of the support structure thereby reducing braking effectiveness. Typically, the assembly of the springs to the support structure requires a secure fastening which may require a difficult manufacturing step such as threading a spring through an opening. Further, when the sleeve must perform the two functions of providing a sliding surface and providing support, it can be optimized for neither function. These are some of the objections this new invention overcomes.